In magnetic resonance imaging, atomic nucleus spins of an object positioned in a static magnetic field are magnetically excited with an RF (radio frequency) pulse at a Larmor frequency. Magnetic resonance imaging is an imaging method to generate an image from data of nuclear magnetic resonance (NMR) signals generated as a consequence of the excitation.
When an examination using a magnetic resonance imaging apparatus (“MRI apparatus” hereinafter) is conducted, a receive coil for receiving NMR signals from protons is attached to an object. The receive coil is connected to the MRI apparatus via a cable. If the cable and the receive coil get too close to a bore having an approximately cylindrical shape, an unbalanced current flows in the cable and the receive coil. At this time, the cable and the receive coil may generate heat and short-circuit.
To prevent an unbalanced current from flowing in the cable and the receive coil, a balance-unbalance converter (“balun” hereinafter) may be attached to the cable or the receive coil. A balun absorbs an unbalanced current by its resonance circuitry to prevent the unbalanced current from flowing in the cable and the receive coil. However, if a balun gets too close to the side wall of the bore of the MRI apparatus, an unbalanced current flowing in the balun will increase, and the balun may generate heat.